featherwinglove wrote: Sun Dec 23, 2018 6:39 am
Nightinggale wrote: Sat Dec 22, 2018 7:35 pm
* The actual speed is the speed of light, which is 299.792.458 m/s. Depending on the metal, it can lose a little bit of speed, but it's still very close to that number. 300.000.000 is a common approximation as it's often close enough and it makes the calculations much easier, like allowing all calculations in this post to be done without a calculator. It doesn't really matter if the answer is 4k or 5k km/tick. Both are way too fast to justify Factorio not assuming the speed to be instant.
Actually, the travel speed depends on the dielectric constant of the volume around the wire and switching speeds depend on capacitance. This is why microchip manufacturers are trying to reduce the dielectric constant in the interconnect insulators, but increase it in MOSFET (generic gate-dielectric-channel type transistor however it's formed) gate insulator. It is usually a significant fraction of the speed of light, but is still significantly slower.
You are right, but that doesn't mean I'm not right at the same time. The thing is you are talking about tightly packed wires next to each other with insulation in between with a not insignificant dielectric constant. I on the other hand only wrote about the power grid. This is uninsulated copper wires in mid air and without insulation at all, we can ignore the capacitance in the wires.
Since the capacitance in wires can be ignored for the Factorio power grid, I decided to not mention it at all. I could also have mentioned that the spread of current in a wire depends on frequency, meaning AC doesn't scale linearly. Twice the cross area of a wire will allow twice the current for DC, but less than twice the AC current. That's another detail I decided not to include in order to keep it simple.
Capacitance in wires leads to increased power loss for AC wires, which is actually the main reason why high voltage wires tend to be uninsulated and placed far into the air. It's not because it's the cheapest way to build wires. That's just a bonus. The concern is about how much power a powerplant has to produce to power your 100 W computer and uninsulated wires are the best for that job.
Underwater cables suffers from huge capacitance in the insulation and unless they are fairly short, they tend to be DC because DC doesn't change voltage, hence doesn't suffer from cables not wanting to change voltage. Underwater cables have a certain distance where AC just won't pass as in 100% power loss. The distance is rather short, like a few hundred km. DC doesn't suffer from this and the UK is building a power cable to Iceland because Icelandic powerplants run on steam coming out of the ground, hence no fuel or emissions.
featherwinglove wrote: Sun Dec 23, 2018 6:39 am99% of the reason we have AC instead of DC on large scale power grids is because it allows us to use non-switching transformers to step the voltages up and down (and I can't remember what the other 1% of the reason was.)
The primary reason is historical. Edison built the first powerplant in Pearl street on Manhattan. It delivered 110 V DC. This meant low voltage, hence high current and the distance from powerplant to consumer was 100-200 meters (or yards. The uncertainty is much greater than the difference between a meter and a yard). Westinghouse went with AC because transformers allows high voltage, hence low current and low power loss. This allows consumer and powerplant to be placed in different states. The problem was that DC motors worked ok while AC motors was unusable. A Westinghouse employee named Nikola Tesla figured out how to produce a 3 phased motor, which could compete against the DC motor. Westinghouse then pushed forward with poly phased power as it was called back then. It won the war of the currents, resulted in country wide AC power grids in most countries and ages after everything was up and running in large grids, somebody invented a way to make a "DC transformer". The need was however not great as it doesn't make sense to replace existing and working AC for DC, particularly because the price of doing so would be really high.
DC is used for special cases, like underwater/underground cables, connecting two powergrids not using the same frequency or using the same frequency, but are out of phase etc. This requires another invention (or 2), which allows moving between DC and AC.
If you wonder where such conversions takes, place, then here are some examples. Back in the day when power grids were just for a city and cities weren't connected, one Japanese power company bought generators in America and another bought in Europe. The result is that today Japan has both 50 and 60 Hz, which is causing problems, but not significantly enough to change. Instead transformer stations goes AC-DC-AC to bridge the frequency areas. Another example is the fact that Scandinavia runs 50 Hz like the rest of Europe, but being isolated prior to introduction of underwater cables, the voltage doesn't peak at the same time, meaning connections have to use the Japanese approach even though both sides are 50 Hz. There is also the fact that railroads doesn't always use the same frequency as the power grid. Germany use 16.7 Hz for trains (again for historical reasons. Early AC engines got hotter with high frequency and 50 Hz would melt the cobber in such high power motors and Austria/Germany invented/pioneered AC trains, hence using a much older standard than other countries, like pre WW1 vs other countries deciding on frequency during the 60s to 80s), meaning power to overhead wires have to use AC-DC-AC conversions here as well.
featherwinglove wrote: Sun Dec 23, 2018 6:39 amWire resistance cares about current and not voltage, while the total power is the product of the two.
Power delivered: P = U*I, as in power(W) = Voltage(V) * Current(A)
Power loss per km/mile/whatever: P = k*I*I (Ohm's law combined with the previous equation)
k is a constant based on the thickness of the wire. This means lowering k makes the wire thicker, hence more expensive and less bendy, which in turn makes it more difficult to put it up.
Combine this and you see that you want a low I. Since you want a constant U*I, you naturally want a high U, hence high voltage.
This is getting way off topic. The fact remain that for power grids (and in general), Factorio doesn't have the size to make it make sense to consider the speed of electricity in the power grid to be anything other than instant.